Two-step controlled flow gasification process

ABSTRACT

IN A SINGLE VESSEL REACTOR A HEAVY HYDROCARBON FUEL IS STRIPPED OF VALUABLE LIGHT HYDROCARBONS AND HEATED TO A TEMPERATURE BETWEEN 1100* AND 1300*F. IN A HEATING ZONE BEFORE A PORTION IS TRANSFERRED TO A GASIFICATION ZONE TO BE SUBSTANTIALLY COMPLETELY CONVERTED TO A HYDROGEN   AND CARBON OXIDE-CONTAINING GASEOUS STREAM, THE RATE OF TRANSFER BEING CONTROLLED BY THE PRESSURE DIFFERENTIAL BETWEEN THE TWO ZONES.

May 15. 1 7 J. F. ZEMAITIS. JR 3,733,136

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United States Patent Oflice 3,733,186 TWO-STEP CONTROLLED FLOW GASIFICATION PROCESS Joseph F. Zemaitis, In, Morristown, N.J., assignor to Esso Research and Engineering Company Filed Apr. 6, 1971, Ser. No. 131,728 Int. Cl. Cb 49/10; C10j 3/00 U.S. Cl. 48-202 7 Claims ABSTRACT OF THE DISCLOSURE In a single vessel reactor a heavy hydrocarbon fuel is stripped of valuable light hydrocarbons and heated to a temperature between 1100 and 1300 F. in a heating zone before a portion is transferred to a gasification zone to be substantially completely converted to a hydrogen and carbon oxide-containing gaseous stream, the rate of transfer being controlled by the pressure differential between the two zones.

BACKGROUND OF THE INVENTION This invention relates to a novel two-step, controlled flow gasification process for producing hydrogen, carbon oxide-containing gases and valuable light hydrocarbon materials.

In another aspect this invention relates to a novel integrated fluid coking-gasification process.

With the increased need for hydrogen in many phases of petroleum refining the petroleum industry has been desirous of finding an economical source for this needed hydrogen. It was soon recognized that gasification of heavy hydrocarbon materials, especially fluid coke, could be an economical source of the needed hydrogen. Furthermore, under certain operating conditions gasification of the coke resulted in a high B.t.u. fuel gas.

In an effort to utilize the fluid coke for hydrogen production gasification reactors were constructed to tie in with existing two vessel fluid coking process systems. For example, see U.S. Pat. 2,527,575; U.S. Pat. 2,640,034; U.S. Pat. 2,657,986; U.S. Pat. 2,657,987; US. Pat. 2,741,- 549; U.S. Pat. 2,885,350; U.S. Pat. 2,888,395; U.S. Pat. 2,894,897; and U.S. Pat. 2,917,451. However, such three vessel systems have several economic drawbacks. First, the cost for constructing a vessel for handling the high temperatures necessary in a gasification process is extremely expensive. This, added to the cost of high temperature transfer lines, high' temperature valves and cyclones needed in the process result in a large initial capital expenditure.

To improve the efficiency and lower the capital cost several integrated fluid coking-coke gasification processes have been proposed. Typically they are a two vessel system where the heavy hydrocarbon material is coked in the first vessel and then sent to a second vessel to be gasified. Such a system is described in patent application Ser. No. 880,219 by A. L. Saxton, filed Nov. 26, 1969, now U.S. Pat. No. 3,661,543. In this system the coke produced a conventional fluid coking reactor was injected into a high temperature or gasifying-zone (-1800 F.) to produce hot hydrogen-containing gases (principally H and CO). These hot gases are then passed through a gas distributor apparatus to a lower temperature zone in order to heat this zone and to maintain it in a fluidized state. However, with this process design there is a possibility that the lower temperature zone bed might dump into the high temperature bed as a result of possible combustion under the gas distributor and/or erosion by the particles in the gas stream destroying the gas distributor. Also this design does not reduce the need for high temperature slide valves which are not reliable under the severe process conditions to which they are subjected. Furthermore, the valu- 3,733,186 Patented May 15, 1973 able light hydrocarbon material on the coke is burned in the high temperature zone and hence not recoverable.

It is therefore an object of this invention to overcome the hereinbefore stated prior art problems in a process for producing a hydrogen and carbon oxide-containing gaseous stream.

These and other objects of this invention will become apparent from the hereinafter description of the invention.

SUMMARY OF THE INVENTION In its broadest aspects a novel, two step, flow control gasification process is provided which converts a low value heavy hydrocarbon material, such as coke, into hydrogen and carbon oxide gaseous streams, as well as valuable light hydrocarbons in a gasifier reactor. The heavy hydrocarbon material is introduced into a low temperature heating zone, operating at a temperature between about 1100 and about 1300 F. (preferably about 1150 E), where it is contacted with a bed of fluidized particles and a free oxygen-containing gas, such as air or oxygen. This contacting results in the heating of the heavy hydrocarbon material to the desired temperature of between about 1l00 and about 1300 F. (preferably, 1150 F.), as well as, the production of carbon oxide-containing gaseous stream and valuable light hydrocarbons such as methane.

A portion of this hot material may be removed from the low temperature heating zone to be used as fuel or to provide heat in another process. A second portion of the hot material is passed to the high temperature gasifying zone of this process. The quantity of material passed to the gasifying zone will be substantially the same amount that is converted by gasification to hydrogen and carbon oxide-containing gaseous streams. In this way only the desired valuable gaseous products are obtained and no heavy hydrocarbon residua, such as coke, is produced. Under the following gasification conditions:

1 Above atmospheric.

the desired flow rate from the low temperature heating zone to the high temperature gasifying zone can be obtained by maintaining the pressure on the heating zone side of the orifice connecting the two zones between about 1 and about 5 p.s.i.g. greater than in the gasifying zone. This pressure difference is obtained by controlling with a cyclone or other means the rate at which the gases produced in the low temperature heating zone are allowed to escape this zone, as well as, by the bed height in the heating zone. By removing the gases at a rate slower than the rate at which they are produced a pressure within the heating zone may be built. Once the desired pressure level is reached the flow rate of escaping gases is set, thus providing for a smooth, continuous operation.

In a preferred embodiment of this invention the gases produced in the gasifying zone are contacted with the escaping gases from the heating zone. Since the heating zone gases are cooler than the gasifying zone gases there will be a heat exchange between them. By proper contacting the resulting gases can all be at a temperature less than 1600 F. This is very advantageous since these gases must pass through a cyclone device to remove any entrained particles before further processing. At temperatures below 1600" F. a low temperature cyclone may be employed which is very dependable over long periods of operation. At temperatures above 1600 F. cyclone devices are not reliable.

In a most preferred embodiment of this invention the controlled flow, two step gasification process is integrated with a fluid coker so as to use the coke produced in the fluid coker as feed for the gasifier reactor.

BRIEF DESCRIPTION OF THE DRAWING FIG. I schematically illustrates one preferred embodiment of the invention wherein the two zones in the second reactor adjoin one another.

FIG. II represents a cross-sectional view of an alternate preferred embodiment design for the second or gasification reactor used in the process of this invention.

PREFERRED EMBODIMENT OF THE INVENTION The reaction of carbon with certain gases such as air, oxygen or steam under certain conditions will produce hydrogenand carbon-containing gases. For example, note the following possible reactions These reactions unfortunately are not easily controlled and are reversible under certain conditions. Furthermore, some of the reactions inhibit other of the reactions depending on the reaction conditions. A publication entitled, Coal Gasification, by Von Fredersdorlf & Elliott found in the Chemistry of Coal Utilization (supplementary volume) edited by Lowry gives an excellent insight into the complex interplay between these reactions. Such an insight is necessary to appreciate the process features of this invention.

In both embodiments as shown in FIGS. I and II a heavy hydrocarbon material, preferably a vacuum or atmospheric residua, is introduced into fluid coker 101 by line 102. There it contacts a fluidized bed of particulate matter in coking bed 103 said bed being fluidized by a gaseous stream such as steam or air introduced into the lower part of fluid coker 101 by line 104. The reaction between the gaseous stream, residua and coking bed particles results in the production of light hydrocarbon prod ucts which leave the coking bed 103 by cyclone 105 and enter into a fractionator 106. In the fractionator the light hydrocarbon products are acted upon to produce a gas, a naphtha fraction, a gas oil fraction and a heavy residua fraction which are removed from the fractionator by line 107, line 108, line 109, and line 110 respectfully. The residua in line 110 may be recycled to the fractionator 106 by lines 111 and 112, or it may be blended with the feed in line 102 by line 113 and introduced into coking bed 103. The reactions in coking bed 103 also results in the formation of fluid coke on the particulate matter comprising the bed, a portion of which is transferred by line 114 with the aid of lift gas, such as steam, air or oxygen, from lines 115 and 116 to the gasification reactor 117.

Inert particles such as silica, alumina, zirconia, magnesia, alundum of mullite, or synthetically prepared or naturally occurring material such as pumice, clay, kieselguhr, diatomaceous earth, bauxite and the like may be used to form bed 103, but preferably bed 103 will comprise coke particles, and more preferably coke particles whose diameters are between 40 and 400 microns.

Coking bed 103 is maintained at a temperature between 900 and 1100 F., preferably about 950 F., by hot coke introduced from the low temperature heating zone 118 in reactor 117. If also desired, the feed in line 102 may be preheated by a furnace (not shown) before being introduced into coking bed 103.

In FIG. I the coke at a temperature of about 950 F. is introduced into low temperature heating zone 118 of reactor 117. Heating zone 118 is separated from a high temperature gasifying zone 119 by walls 120 and 120a, except for opening 121 which allows the coke making up heating zone bed 122, maintained in a fluidized state by the air or oxygen from line passing through gas distributor 125, to pass into gasifying zone bed 123 maintained in a fluidized state by steam from line 131 and air or oxygen from line 132 passing through gas distributor 125. Heat ing zone 118 is also separated from gasifying zone 119 by an upper wall or ceiling 124. Attached to the ceiling 124 is low temperature cyclone 126 with dipleg 127 which allows the gases and valuable light hydrocarbons produced in heating zone 118 to esca e to gasifying zone 119 and eventually to leave reactor 117 by line 128 and cyclone apparatus 129.

The contacting of the coke with the bed particles and the gases from line 130 results in the production of carbon oxide containing gases, as well, as the heating of the coke from fluid coker 101. Under the process conditions described hereinafter the bed temperature in heating zone 118 is maintained between about 1100" and about 1300 F. Preferably the temperature is maintained at about 1150 F. to allow the recovery of valuable light hydrocarbon materials embedded on the coke particles such as methane, ethane, and ethylene, that would normally be burned at higher temperatures.

A portion of the hot coke from bed 122 is recycled by line with the aid of lift gas from line 136 to fluid coke 101 in order to provide the heat requirements of that reactor. If necessary or desired this recycled coke can be heated to higher temperatures by a free oxygen-containing stream from line 137 before it enters the fluid coker.

Another portion of the hot coke from bed 122 is circulated through orifice, or orifices, 121 into gasification bed 123. The amount of the second portion will be substantially the same amount of coke as is being converted to hydrogen and carbon oxide, containing gases in gasifying zone 119.

The temperature Within bed 123 should be maintained between 1300 and 2200 F. in order to achieve gasification of the coke. Better gasification rates are obtained at the upper end of the temperature spectrum if no gasification catalyst is employed. However at temperatures above 2000 F. the cost of reactor 117 becomes prohibitive. Also at this temperature range the amount of oxygen needed to maintain that temperature level adds greatly to the process cost. For these reasons temperatures between l600 and 2000 F. are preferred, and about 1800 F. most preferred. The temperature may be maintained at the preferred level if the steam rate is between 0.04 and 0.20 mole H O/moles C/hr. and the oxygen or air rate is between 0.05 and 0.20 mole O /mole C/hr. Most preferably the rates will be between 0.05 and 0.10 mole H O/ mole C/hr. and between 0.1 and 0.15 mole O /mole C/hr.

To further insure that adequate gasification occurs and that no oxygen can break through bed 123 to cause an explosion, bed 123 should be of a depth greater than 10 feet per 2 ft./ sec. of the oxygen rate.

Under these gasification conditions it is desirable to operate the process in the heating zone under the following conditions:

At these conditions bed 122 can be maintained in a satisfactory fiuidized condition to insure adequate contact between the coke from the fluid coker, the particles in bed 122 and the free oxygen-containing gases from line 130.

The light hydrocarbon materials removed from the coke and the carbon oxide-containing gases produced in heating zone 118, along with the unreacted gases from line 130 rise to the top of zone 118. There a portion of these gaseous products are removed from heating zone 118 by a flow control means such as low temperature cyclone 126. The entrained solids in the escaping gaseous products are returned to the heating zone by dipleg 127. The

rate at which the gaseous product is allowed to escape is controlled by cyclone 126 so that the pressure within the heating zone is about 1 to about 5 p.s.i.g. greater than the pressure in gaifying zone 119. By maintaining this pressure difference the desired coke flow from the heating zone to the gasifying zone can be obtained.

In a more preferred embodiment the cool, about 1100" F.) gases and light hydrocarbon material from heating zone 118 blend with the hot (about 1800 F.) hydrogenand carbon oxide-containing gases rising from gasifying zone 117 in the top 133 of gasifying zone 119 before leaving reactor 117. This contact results in a heat transfer from the hot gases to the cooler gases and light hydrogen products. By the time the mixture gets to cyclone 129 the temperature is about 1600 F. Because of this drop of about 200 F. the cyclone will be more dependable. If desired the gases and light hydrocarbons could be cooled to a greater extent by various known cooling ap paratus (not shown) before they get to cyclone 129. The fines or other heavy particles which are mixed in the gas stream are separated in cyclone l24-and returned to bed 122 by dipleg 134.

In FIG. II the fluid coke from coker 101 is injected into heating zone 138, which in this alternate configuration is located in about the center of gasification reactor 117, to form heating zone bed 139. Bed 139 is separated from gasifying bed 144 by walls 153 and 154, and separated from the gases produced in gasifying zone 143 by an upper wall or ceiling 155 which supports low temperature cyclone 147. As in FIG. I heating zone bed 139 is maintained in a fluidized state by a fluidizing gas, such as air or oxygen. The fluidizing gas is injected into zone 138 by line 140 where it passes through a gas distributor 141 into heating zone bed 139.

As before the velocity and quantity of fluidizing gas injected into zone 138 must be adequate to build up enough gas pressure within zone 138 to force the stripped coke in bed 139 through openings 142 and into gasifying zone 143 at the desired rate, to strip the valuable light hydrocarbons from the cake comprising bed 139 before they are burned and to maintain the bed at a temperature between 1100 and 1300" F., preferably 1150 F. This may be accomplished with about the same gas velocity as used in FIG. I.

The coke which enters gasifying zone 143 makes up gasifying zone bed 144 which like bed 139 is maintained in a fluidized state by fluidizing gases such as steam and air or oxygen. These fiuidizing gases are injected into zone 143 by line 145 (steam) and line 146 (air or oxygen) where it passes through gas distributor 141 into gasifying'bed 144.

The velocity and rate at which the fluidizing gases are injected into bed 144 must be sutficient to generate a substantial quantity of hydrogenand carbon-containing gases for the process to be economically attractive, to maintain bed 144 at a temperature between 1300 and 2200 F., but not too great so that oxygen may break through bed 144 significantly increasing the chance of an explosion. This is accomplished by using the steam and free oxygen rates and velocities stated with regard to the process in FIG. I.

As before the gases produced in heating zone 138 escape through cyclone 147, equipped with dipleg 156 to return to bed 139 any fines that may have been carried up by the rising gases, into the upper portion 148 of gasifying zone 143. There these gases are mixed with the hotter gases produced in the gasifying zone bed 144 before the mixture is removed from reactor 117 by cyclone 149, equipped with dipleg 150 to return to bed 139 any fines that may have been carried up by the rising gases, and line 151.

Means 152 are provided to recycle a portion of the stripped coke to coking bed 103 in the fluid coker 101.

The process as described in both embodiments also has several advantages over previous single vessel designs dealing with other hydrocarbon treating processes with regard to bed fluidization. According to the designs of this system there is not a two way flow of the coke; i.e., from the heating zone to the gasifying zone and then back to the heating zone. Two way flow designs have not been successful because such a system depended on maintaining specific differences in bed levels to sustain the particle flow where both beds were under the same gas pressure. This could only be accomplished by lowering the gas velocity to such an extent that the low temperature bed could not be maintained as a fluidized bed. This resulted in agglomeration of the particles in this bed which agglomeration plugged the openings between the beds. The problems associated with these old single vessel designs, such as found in US. Pat. 2,445,327, have been overcome by maintaining the beds under different gas pressure and using this gas pressure, which is much easier to control than bed level, to transfer the coke from one bed to another. In this manner fluidization of the bed is simplier since a broader range of gas velocities and gas rates can be utilized.

Having now fully set forth and illustrated and specific examples of the same given, what is claimed as new, useful and unobvious is:

1. In a gasification process for converting a carbonaceous material into a hydrogen-containing gas by contacting said carbonaceous material with steam in a gasification zone operated at temperatures between about 1300 and 2200 F. and pressures between about 5 and 50 p.s.i.g., the improvement which comprises:

(a) introducing a carbonaceous material into a heating zone contiguous to said gasification zone, both of said zones being disposed in a single vessel and being separated from each other by separating means including an inner wall having at least one opening to permit passage of carbonaceous material there through;

(b) reacting the carbonaceous material in said heating zone at a temperature between about 1100 and 1300 F. with a free oxygen-containing gas to produce a carbon oxide-containing gas and heated carbonaceous material;

(0) maintaining a higher pressure in said heating zone than in said gasification zone by controlling the flow rate of said carbon oxide-containing gas escaping from said heating zone whereby a portion of said heated carbonaceous material is passed from said heating zone to said gasification zone, and

(d) converting said portion of heated carbonaceous material in said gasification zone into a hydrogencontaining gas.

2. The process of claim 1, wherein the (flow rate of said carbon oxide containing gas from said heating zone is controlled in such a manner as to retain a sufficient amount of said carbon oxide-containing gas in said heating zone to provide the pressure required to pass said portion of heated carbonaceous material from said heating zone to said gasification zone.

3. The process of claim 1, wherein the carbon oxidecontaining gas is removed from the heating zone at a rate slower than the rate at which it is produced.

4. The process of claim 1, wherein the pressure in the heating zone is between about 1 and about 5 p.s.i.g. greater than the pressure in said gasification zone.

5. The process of claim 1 wherein the carbonaceous material is coke.

6. In an integrated fluid coking-gasification process, wherein coke produced in a coking zone is subsequently completely converted 'to a hydrogen-containing gas in a single vessel, two zone reactor, the improvement which comprises:

(a) passing a portion of fluid coke from a fluid coking zone to a heating zone contiguous to a gasification zone, said heating zone and said gasification zone being located in said single vessel reactor and being separated by separating means including an inner wall having at least one opening to permit passage of coke therethrough;

(b) reacting said coke in said heating zone at a temperature between about 1100 and 1300 F. with a free-oxygen-containing gas to produce a carbon oxide-containing gas and heated coke;

(c) maintaining a higher pressure in said heating zone than in said gasification zone by controlling the fiow rate of removal of said carbon oxide-containing gas from said heating zone, whereby a portion of said heated coke is passed from said heating zone to said gasification zone, and

(d) contacting said portion of heated coke in the gasification zone with steam introduced therein at a rate between about 0.04 and 0.20 mole H O mole C./hr., and with free oxygen at a rate between about 0.05 and about 0.20 mole 0 mole C./hr. at a temperature between about 1300 and 2200 F. at a pressure be- References Cited UNITED STATES PATENTS 2,445,328 7/1948 Keith 48205 X 2,527,197 10/1950 Rollmann 48206 2,600,430 6/1952 Riblett 48206 X 2,700,644 1/1955 Lefier 201-31 X MORRIS O. WOLK, Primary Examiner D. G. MILLMAN, Assistant Examiner US. Cl. X.R. 

